Puncture force

The effect of relative humidity in the domain between 30 and 98% and of the film thickness from 0.13 to 0.32 mm on the puncture force and deformation can be observed in Figure 26.1. It can be seen that the increment of the relative humidity of conditioning provoked the reduction of the puncture force and the increase of puncture deformation following an exponential behavior, according to Equation 26.3 ... 

The effect of the relative humidity of conditioning on the puncture force and deformation can be related to the increase of the matrix hydration considering that gelatin and glycerol are both hydrophilic. The consequent... 

Puncture force (a) and puncture deformation (b) as function of the relative humidity of conditioning and film thickness in gelatin-based films. 

However, it was observed that, in general, the increment of the film fhickness provoked an increase of ifs mechanical resistance, that is, increased the puncture force, and af fhe same time implied a reduction of fhe deformation capacity. However, these effects are dependent on the relative humidity of condifioning, cerfainly as a function of the possible structural alterations within the polymeric matrix. 

The properties of gelatin-based films are strongly influenced by the film thickness and the conditioning conditions. It was verified that an increment of the relative humidity provokes a reduction of the puncture force and an increase of the pimcture deformation. The temperature also affects the water vapor permeability of the films, but this effect depends on the film thickness. 

The puncture force F at rupture is related to the tearing energy Ti by the equation... 

Puncture Force energy (Ib/mil) energy (in-lb/mil) 7.1 21 Exxon Method... 

Graph 30-02. Puncture force and energy of various poiyoiefins and ExxonMobii Exact P0P.i ° ... 

Puncture Force The minimum foree required to puncture a flat plastic material, sueh as film, or textile with a pointed member, such as pyramid, at a slow rate of loading. 

Only few studies have been reported on the effect of the addition of cross-links on film properties. Chemical cross-linkers such as formaldehyde, glyoxal or glutaraldehyde were efficient in enhancing the maximum puncture force of films made from cotton seed proteins. Brault et al introduced cross-links between aromatic compounds (i.e. dityrosine) in caseinate films by exposing them to y-ionisation. Puncture strength and puncture deformation were both increased but this effect was very dependant of the ratio glycerol/protein. 

Where membranes are used in the ground as a vertical barrier they can be subject to high stresses and puncture forces from the surroxmding groxmd, settlement of backfill causing drag down etc. Very robust materials and protection must therefore be provided (see Card, 1995 Privett et ah, 1996). 

While replacing a steam valve on a lumber manufacturing site, a maintenance worker was exposed to a nail on a wooden crate. The worker accidentally grabbed the crate where the nail was protruding and the top layer of leather in his glove was tom. Luckily for the worker, the layer beneath the leather was able to stop the puncture force of the nail, and the worker did not sustain any trace of an injury. 

Fp = geomembrane puncture force (N), foMs = thickness of a geomembrane in contact with a stone (m), tcMp = thickness of geomembrane in contact with a test probe (m), and = strain function. 

---